Abstract: Through the five engineering examples, the possibility of using wind-driven and variable-speed pumps instead of regulating the damper valve to realize the regulation of the wind and water system in the heating and air-conditioning system is discussed. Analysis shows that doing so can save operating energy, while improving the quality of the system regulation, the initial investment of the system will generally not increase. Pump and fan energy consumption accounted for about the total energy consumption of heating and air conditioning system 40? About 1/3 of these energy consumption is consumed by various regulating valves, but such a large price does not bring about good regulation effects, but instead leads to many problems in the system. The use of variable speed blowers and variable speed pumps as an adjustment means saves on energy consumption and eliminates many of the difficulties in adjustment. Keywords: frequency conversion water system wind system variable speed pump variable speed fan 1. Introduction In the HVAC project, the use of a large number of wind valve water system to adjust the volume of air flow to meet the required conditions. Their adjustment principle is to increase the system's resistance to consume excess pump or fan pressure head, to achieve the purpose of reducing the flow. Therefore, the regulatory role of these regulating valve is to consume fan or pump at the expense of running energy. At present, HVAC project more and more use of automatic control system. To achieve self-control, many damper valves also use electric actuators. The current good quality electric valve price of thousands or even tens of thousands. Electric damper also need a few thousand dollars. Electric damper valve costs often account for more than 40% of the total cost of the control system. Can change the composition of the system, reducing the use of these energy-consuming, expensive valves, using other means to achieve the regulation of the flow? Fan pumps and dampers are one-to-one correspondence between the two types of flow control equipment. Fan pumps provide fluid power, while damper valves consume excess fluid. Therefore, if the fan pump instead of air valve, not to install additional valves at the energy surplus, but in insufficient energy to install additional pumps or fans, by adjusting the fan pump speed, the same system can be achieved flow regulation. At this point due to the reduction of the control valve, which reduces the energy consumed by the valve, thus reducing energy consumption. At the same time, the current variable speed fan, pump prices and the same flow of electric damper, water valve prices are close to, or even lower, so the initial investment will not increase. From this point of view, this article gives a few examples of replacing the valve with a pump, and then further discuss the significance of this program on the HVAC project and issues to be noticed in order to arouse the discussion of everyone. 2. Case Study 2.1 Flow Control of a Simple System Figure 1 shows a simple system for controlling the circulation flow. The pump P provides power to circulate water through valve V, pipe and user U. Fig. Figure 2 shows when the valve is fully open, the pump speed n = n0 when the system operating point. At this point, the flow rate G0, pump efficiency η0, that is the highest point of efficiency. To reduce the flow in half, one way is to close the valve to make the equivalent resistance curve of the pipe shift to the left, as shown in Figure 2. At this point the efficiency of the pump is reduced to η1 and the pressure rises to p1. Due to the pressure increase, the efficiency is reduced, so the pump consumption is reduced by only 20% to 30% even though the flow rate is reduced to half. At this time, the pipe network except for the valve consumes only the pressure drop p0 / 4 because of its resistance characteristics. The remaining part of 3 (p0 + (p1-p0)) / 4 are consumed in the valve, which consumes 80% of the pump consumption, which is why the control valve consumes most of the energy consumption of the pump basis. In addition, the instability caused by the pump working point offset, the valve clearance small after the large and noise caused by pressure drop, have a negative impact on the system. If the same, but the pump speed down to 50%, Figure 2 at the same time given the working conditions at this time, then the resistance characteristics of the pipe network unchanged, pump down the curve, the pump efficiency will still Is η0 and pressure p2 is p0 / 4. In this way, after reducing the flow pump consumption is only 1/8 of the original, with a very significant energy saving effect. At the same time, due to the pump operating point and valve position have not changed, so the system is stable, and there will be no throttling noise. Figure 1 Simple water circulation system Figure 2 Adjusting the valve or adjusting the speed to change the flow This simple example shows: (1) When the regulating valve is adjusted, it will consume most of the hydrodynamic force of its branch. And due to changes in the pipe network resistance characteristics, the pipe network in the work of mechanical shift point, in most cases this will lead to reduced efficiency. (2) When using variable speed mode to adjust the flow rate, pump or fan power consumption can be proportional to the third power flow changes. And due to the same system of resistance characteristics, pump or fan operating point unchanged, so the same efficiency, pumps, fans and systems can work stably. (3) to adjust the pump or fan speed to adjust the flow rate should be the best way to adjust. 2.2 Hot water supply network Figure 3 is a simple hot water supply system. When the user requests the same pressure head when the hydraulic pressure chart shown in Figure 4 solid line. Figure 3 heating water network diagram in the figure below the dotted line for the user to consume the capital pressure head, while the above part of the dotted line is consumed by the valve. If the system is designed properly and the pump is properly selected, the residual pressure at the furthest end user is exactly the pressure head it needs. The valve V5 is fully open and consumes little energy. In this case, if the flow of each user is equal and the distance between them is equal, the friction on the main pipe is the same and ignores the resistance when the valve is fully open. For n users, the energy consumed by the valve V1 and the total energy consumed by the outdoor pipe network The percentage EV1 is: EV1 = (1 / n) × ((n-1) / n) The percentage of the energy consumed by the kth valve to the total energy consumption of the user's outdoor network EVk EV1 = (1 / n) × -1) / n) The total energy consumed by the first n-1 valves is: (n-1) / (2n) is approximately equal to 50% when the number of hot users is enough, that is, Half of the branch by the control valve consumed. On the average user's side, the lift actually needed is only 20% to 30% of the circulation pump's lift, that is, the external network consumes 70% to 80%. Therefore, the total pump from 35% to 40% of the energy consumed by the regulating valve. Sometimes for safety's sake, the pump head should be selected larger, and then through the valve V0 Figure 3 the excess part of the consumption. As a result, more than half of the pump consumption of the regulating valve in the general hot water heating network is consumed. If the switch to Figure 5 way to connect the hot water pipe network, users installed at the user back to the booster pump, instead of regulating valve to reduce the head of the main circulating pump, so that it will only assume the heat source and part of the main pipe pressure drop, the user Of the pressure drop and the other part of the main pipe pressure drop by the user within the booster pump to provide, then the hydraulic diagram shown in Figure 6. Figure 5 water pump instead of the valve hot water heating system Figure 6 pump generation valve program hydraulic map at this time no control valve, so there is no control valve loss of pump consumption, the user at all backwater pressure pump lift should be carefully select. If you choose too large, then use the valve to reduce the same energy consumption. However, if the variable speed pump is installed, the flow rate required by each user can be adjusted so that the pump is no longer consumed by the regulating valve, which reduces the operating power consumption by more than 50% even though many pumps are installed. In this case, if the flow rate required by each user changes frequently, the total flow of the whole system also changes within a relatively large range. The total circulating pump can also be controlled by a variable frequency pump, and according to the pressure difference between the supply and return water in the middle of the trunk , 6 midpoint A) to control its speed, so that the point pressure is maintained at zero, the system has a very good regulatory performance and energy saving. Analysis shows that when using the conventional pipe network as shown in Figure 3, if for some reason half of the users shut down and no water supply is needed, the water volume of the non-connected users will increase and the maximum flow rate will increase by more than 50% The pipe network uses the method shown in FIG. 5 and controls the rotational speed of the main circulating pump in the above manner, the water volume of the non-closed users increases by not more than 8% in the same situation, and the hydraulic stability of the system is greatly improved. Further detailed analysis of this area, see [1], this program is ready to start construction in Hangzhou Thermal Power Plant hot and cold cogeneration network, the user for the absorption chiller, domestic hot water heat exchanger, winter is For building heating and domestic hot water. The analysis shows that for this system with a wide range of load changes, this method saves 62% of the pump power consumption and improves the system's hydraulic stability than the conventional method. While also reducing the pressure range of the entire system, which can reduce the pressure pipe network requirements, director of pipe network life. The cost of installing the speed control pump at each user can basically be supplemented by the electric control valve saved by each user and the electricity storage capacity savings saved, so that the total investment may not increase or even decrease.
